The current application is aimed at providing the Principal Investigator with in-depth training in the area of host-microbial interactions along with formal courses at the graduate level to enhance her research and laboratory skills. The expertise of the sponsor and co-sponsor combined with a highly interactive basic-research environment at the Department of Medicine at University of Illinois at Chicago, offer a great training opportunity for the Principal Investigator to achieve her long-term goals in becoming an independent research investigator in the area of host- microbial interactions. The proposed studies are focused to examine the role of anion transport in the pathophysiology of diarrhea associated with infection by an important food-borne pathogen, Enteropathogenic E. coli (EPEC). To date, the mechanism(s) underlying EPEC associated diarrhea are not clear. Diarrhea results from increased secretion or decreased absorption or both. Earlier studies have failed to conclusively show an increase in host secretory responses by EPEC infection. We hypothesized that EPEC-induced diarrhea might involve a decrease in intestinal ion absorptive processes. Our preliminary data showed a decrease in CI'-OH'exchange activity, butyrate transport and Na+ absorbing isoform, NHE3 in response to EPEC infection. The present studies will explore the effects of EPEC infection on Cl'-OH'exchange activity in both in vitro and in vivo models and elucidate the contribution of luminal anion exchangers, DRA (SLC26A3) and PAT-1 (SLC26A6). Studies in Specific Aim 1 will determine the effects of EPEC on Cl'transport in model human small intestinal (Caco-2) and colonic (T84 and non-transformed NCM460) epithelia;along with elucidation of signaling mechanism(s), role of EPEC virulence genes and kinetic parameters of EPEC mediated effects on Cl'transport. Specific Aim 2 will utilize siRNA technology to define the role of DRA and PAT-1 in modulation of CI'-OH'exchange in response to EPEC infection. Specific Aim 3 will critically examine the effects of EPEC on CI'transport in ileum and colon utilizing the in vivo murine model of EPEC infection. The results from these studies will not only increase our understanding of the mechanisms of regulation of human intestinal Cl'-OH'exchangers and their modulation by pathogenic organisms, but will also provide basis for the pathogenesis of EPEC-induced diarrhea which might aid in the development of improved therapeutic modalities in future.